Disclosed herein are precursors and compositions thereof for depositing Group 4 metal-containing films. Also disclosed herein are methods for making the precursors along with methods for depositing Group 4 metal-containing films. With regard to the later, the described method may form a metal-containing film, such as, but not limited to, stoichiometric or non-stoichiometric strontium titanate and barium strontium titanate films using deposition processes such as, but not limited to, atomic layer deposition (ALD) or cyclic chemical vapor deposition (CCVD) that may be used, for example, as a gate dielectric or capacitor dielectric film in a semiconductor device.
With each generation of metal oxide semiconductor (MOS) integrated circuit (IC), the device dimensions have been continuously scaled down to provide for high-density and high-performance such as high speed and low power consumption requirements. Unfortunately, field effect semiconductor devices produce an output signal that is proportional to the width of the channel, such that scaling reduces their output. This effect has generally been compensated for by decreasing the thickness of gate dielectric, thus bringing the gate in closer proximity to the channel and enhancing the field effect which thereby increasing the drive current. Therefore, it has become increasingly important to provide extremely thin reliable and low-defect gate dielectrics for improving device performance.
For decades, a thermal silicon oxide, SiO2 has been mainly used as a gate dielectric because it is stable with the underlying silicon substrate and its fabrication process is relatively simple. However, because the silicon oxide gate dielectric has a relatively low dielectric constant (k), 3.9, further scaling down of silicon oxide gate dielectric thickness has become more and more difficult, especially due to gate-to-channel leakage current through the thin silicon oxide gate dielectric.
This leads to consideration of alternative dielectric materials that can be formed in a thicker layer than silicon oxide but still produce the same or better device performance. This performance can be expressed as “equivalent oxide thickness (EOT)”. Although the alternative dielectric material layer may be thicker than a comparative silicon oxide layer, it has the equivalent effect of a much thinner layer of silicon oxide layer.
To this end, high-k metal oxide materials have been proposed as the alternative dielectric materials for gate or capacitor dielectrics. Group 4-containing precursors may also be used by themselves or combined with other metal-containing precursors, such as, for example, Pb(Zr,Ti)O3 or (Ba,Si)(Zr,Ti)O3, to make high dielectric constant and/or ferroelectric oxide thin films. Because the dielectric constant of metal oxide materials can be made that is higher than that of the silicon oxide (e.g., a dielectric constrant for Al2O3 ranging from 9-11; dielectric constant for HfO2 ranging from 15-26; dielectric constant for ZrO2 ranging from 14-25; dielectric constant from TiO2 ranging from 50-80; and dielectric constant for SrTiO3 or approximately 200), a thicker metal oxide layer having an EOT less than 2 Å can be deposited. As a result, the semiconductor industry requires Group 4 precursors, such as, for example, titanium-containing, zirconium-containing, and hafnium-containing precursors and combinations thereof, to be able to deposit metal-containing films such as, but not limited to, oxide, nitride, silicate or combinations thereof on substrates such as metal nitride or silicon.
Unfortunately, the use of high-k metal oxide materials presents several problems when using traditional substrate materials such as silicon. The silicon can react with the high-k metal oxide or be oxidized during deposition of the high-k metal oxide or subsequent thermal processes, thereby forming an interface layer of silicon oxide. This increases the equivalent oxide thickness, thereby degrading device performance. Further, an interface trap density between the high-k metal oxide layer and the silicon substrate is increased. Thus, the channel mobility of the carriers is reduced. This reduces the on/off current ratio of the MOS transistor, thereby degrading its switching characteristics. Also, the high-k metal oxide layer such as a hafnium oxide (HfO2) layer or a zirconium oxide (ZrO2) layer has a relatively low crystallization temperature and is thermally unstable. Thus, the metal oxide layer can be easily crystallized during a subsequent thermal annealing process for activating the impurities injected into source/drain regions. This can form grain boundaries in the metal oxide layer through which current can pass. As the surface roughness of the metal oxide layer increases, the leakage current characteristics may deteriorate. Further, the crystallization of the high-k metal oxide layer undesirably affects a subsequent alignment process due to irregular reflection of the light on an alignment key having the rough surface.
In addition to minimizing side reactions with the substrate that the Group 4 precursor is deposited upon, it is also desirable that the Group 4 precursor be thermally stable at a temperature of 250° C. or greater. Group 4-containing metal films are typically deposited using a vapor deposition (e.g., chemical vapor deposition and/or atomic layer deposition) process. It is desirable that these precursors are thermally stable during vapor delivery in order to avoid premature decomposition of the precursor before it reaches the vapor deposition chamber during processing. Premature decomposition of the precursor not only results in undesirable accumulation of side products that will clog fluid flow conduits of the deposition apparatus, but also may causes undesirable variations in composition of the deposited gate/capacitor dielectric, high dielectric constant and/or ferroelectric metal oxide thin film. Further, it is desirable that the Group 4 precursors avoid undesirable side reactions with other source reagents, e.g., reagents containing silicon, oxide, nitride, or other metals, such as, but not limited to, Pb and/or Ti. Because some of the Group 4 precursors are solid, it is desirable that these precursors maintain their chemical identity over time when dissolved or suspended in organic solvents. Any change in chemical identity of Group 4 precursor in the solvent medium is deleterious because it may impair the ability of the vapor deposition process to achieve repeatable delivery and film growth.
As previously discussed, the Group 4 precursors in the prior art are mostly solid and have relatively low vapor pressure (e.g., 0.5 torr or below). Of the few Group 4 precursors that are in liquid form that are reported in the prior art, these precursors are typically not thermally stable at temperatures greater than 100° C., which may cause delivery or process issues during semiconductor manufacturing which can include, but are not limited to, clogging of the delivery lines between the source container and reactor and unwanted particle deposition on the wafers.
Accordingly, there is a need to develop Group 4 precursors, preferably liquid Group 4 precursors, which exhibit at least one of the following properties: lower molecular weight (e.g., 500 m.u. or below), lower melting point (e.g., 100° C. or below), and higher vapor pressure (e.g., 0.5 torr or greater).